NEW DELHI, Jan 28 (Reuters) - India's opposition criticised ruling party leader Rahul Gandhi on Tuesday for avoiding any expression of regret for the killings of Sikhs in riots three decades ago, a sensitive issue that threatens to dog him in a tight election due by May.

Gandhi said the government led by his Congress party did everything it could to control the violence against minority Sikhs in retaliation for the assassination of his grandmother, then prime minister Indira Gandhi, by her Sikh bodyguards in 1984.

Nearly 3,000 people were killed in the riots and rights activists accuse the Congress of having turned a blind eye and say some of its leaders helped orchestrate the violence.

"It is tragic that so many died but there is no tribute, no remorse, no apology," said Prakash Singh Badal, the chief minister of Sikh-dominated Punjab state whose party is a member of the main opposition alliance.

Gandhi in a rare interview broadcast on Monday night said the riots were horrible and that some members of the Congress party may have been involved. But they had been punished and the government had, at the time, tried to stop the attacks.

He said he had nothing to do with the violence when asked if he would apologise or at least express regret.

"I think that riots, as all riots, were a horrible event. Frankly I was not in operation in the Congress party," said Gandhi, the fourth generation member of the Nehru-Gandhi dynasty.

Instead, he targeted the opposition's prime ministerial candidate Narendra Modi, accusing his administration in the western state of Gujarat of abetting attacks against Muslims there in another series of riots in 2002.

But Modi's Hindu nationalist Bharatiya Janata Party (BJP), rejected the accusation and said Gandhi was wrong to draw a comparison between the two incidents.

"Congress leaders were seen leading the mobs," senior BJP leader Arun Jaitley said of the 1984 violence. "Sikhs were massacred at thousands of places. Nowhere did the police fire a single bullet to disperse mobs. Cases were not investigated."

"Where did Rahul Gandhi get this idea that in 1984 there was no participation of the state?"

Sikhs make up about 2 percent of Hindu-majority India's population of 1.2 billion.

Indira Gandhi's assassination, in October 1984, was carried out in revenge for her decision to send the army in to flush Sikh separatist militants out of the Golden Temple - Sikhism's holiest shrine - in the northern city of Amritsar in June that year.

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